Most of the approximately 180,000 patients diagnosed with early-stage invasive breast cancer or carcinoma in situ have the option of breast conserving therapy (BCT), a procedure that provides superior cosmetic results compared with total mastectomy [9]. This method of treatment involves a lumpectomy, or the local removal of the primary breast lesion with clear tumor-free margins, typically followed by radiotherapy for optimal management of the disease. Several prospective, randomized studies demonstrate no difference in the 10-year survival of patients undergoing successful BCT versus total mastectomy, making it a viable option for many patients. It has been shown that the presence of tumor in the removed tissue within 1-2 mm of the surgical margin is strongly correlated with the risk of local recurrence. Margins therefore play a key role in the prognosis of the patient with respect to local recurrence of breast cancer and are directly correlated to the success of BCT as a treatment modality. Consequently, there is a need for intraoperative evaluation of the resection front so that immediate re-excision of suspicious margins can be performed, minimizing the necessity for a second surgery down the line.
Any method used to evaluate the surgical margins must be rapid and relatively simple to implement if it is to be used in routine clinical care. The simplest technique for determining margin status is based on visual inspection of the excised tissue for evidence of tumor, a method that leads to incorrect diagnoses, and therefore repeat surgeries or a higher risk of recurrence, in at least 25% of cases. Serial sectioning with standard histopathology provides a definitive diagnosis of margin status, but results may take several days to over a week, meaning the patient will go through a period of uncertainty and then require a second procedure if tumor-positive margins are found. Among intraoperative techniques, frozen section pathology is commonly used but is time consuming and prone to sampling error. Imprint cytology (“touch prep”) and ultrasound are more accurate than gross examination, but they can be time consuming and have limited sensitivity. Current intraoperative margin evaluation techniques all have significant limitations in accuracy and/or time required [10, 11]. These limitations in current methods emphasize the continued need for a real-time, intraoperative tool that can accurately determine the status of breast surgical margins.
Light based methods have the potential to provide automated, fast determination of surgical margin status of the excised specimen while the patient is still in the operating room without disrupting or removing any tissue for such analysis. Although several techniques have been used to investigate breast pathology, including diffuse optical tomography and optical coherence tomography, these techniques have limited applicability in surgical margin evaluation due to their trade-off between resolution and penetration depth, and/or method of contrast. Fluorescence and reflectance spectroscopy have been thoroughly researched for breast cancer diagnosis, but these techniques suffer from lower sensitivity than desired.
Several groups have successfully applied Raman spectroscopy for disease detection, particularly for cancer diagnosis in various epithelial tissues [1-3]. A review of the use of Raman spectroscopy for breast cancer diagnosis are reported by Krishna et al. [12]. The inventors have also conducted a study in which nearly 300 Raman spectra from in vitro breast samples were classified into four histopathological categories with 99% overall accuracy [13], which objectively demonstrates the superiority of Raman spectroscopy for this purpose versus diffuse reflectance and/or autofluorescence. A study on guiding resection with Raman spectroscopy was reported [14]. But it relies on a standard fiber probe configuration and does not consider the need for determining margin status to a depth of 1-2 mm on the excised specimen. All of the studies is focused on diagnosis of breast cancer and not for guidance of therapy or margin assessment.
Therefore, a heretofore unaddressed need still exists in the art to address the aforementioned deficiencies and inadequacies.